Embodiments herein generally relate to printing device calibration, and more particularly to methods that scan the test patches, convert each scanned RGB value to an XYZ pseudo space using a color space conversion equation to produce XYZ values, and produce a resulting TRC.
In order to accurately produce a desired printing quality, it is necessary to know the quality level actually being produced by a printer. A tone response curve, most likely nonlinear due to the halftone design and the xerography, provides an illustration of a printer state at a specific time. A calibration tone reproduction curve (TRC) is a transfer function that brings the printer response to a desire state, for example, a linear relationship that produces linear output in density by giving a linear input. If the tone response curve is known, the calibration TRC can be computed and used to compensate for the nonlinearities of the printer. The printer response may change frequently. Thus, to accurately assess the performance of the printer, the tone response curve must be measured frequently in a calibration process.
Therefore, the printing system can be periodically calibrated to achieve color consistency for each of the printers of the same modality. To calibrate the printing system, generally a master printer is first calibrated with a spectrophotometer and a target value or set of target values (referred to herein as an aim curve) is generated for the master printer. The aim curve approaches an ideal or desired color response for the printer that, due to constraints of the printer and/or toners used, is not possible to reproduce exactly. The same aim curve is used in the calibration of the other printers.